We own the core technology of H series light curtain and invention partent.The controller box has 8 channel switches with LED. In normal working condition, all the switches light up( please make sure all of them are pressed). Every switch controls corresponding few diodes of each single board respectively. When an object blocks the infrared beam between the emitter and receiver line, or some diode is broken that can not receive the beams, the blocking signal will tell the corresponding switch bliking. The buzzer will alarm for consecutive 20 second block. In this case, all you need to do is to press the blinking switch to shut off the broken diode, while the other diodes keep working and elevator return to work. It gives convenience both to the elevator user and the repairman.